Free Essay: Quality Improvement of an Injection-Molded Product Using Design of Experiments

Published: 2022-05-24
Free Essay: Quality Improvement of an Injection-Molded Product Using Design of Experiments
Type of paper:  Research paper
Categories:  Engineering
Pages: 4
Wordcount: 911 words
8 min read

Injection molding refers to a production process used in the production of large quantities of plastic materials. The process involves the melting of materials, and injection into a mold before being allowed to cool and solidify, thus taking a desired shape or form. Usually, the injection is done at high pressure to leave no room for bubbles and airbag formation. The shape of the mold is typically designed to be the invert of the required final product. The efficiency and degree of precision that this technique allows making it suitable for the production of a wide range of quality products, from small household products to products such as car parts. During the manufacturing process, however, various flaws and defects may be experienced, leading to the compromise of quality in the finished product. The paper aims to address some of the methods used in the improvement of the quality of products made through this process and the minimization of defects.

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There are several types quality compromising defects associated with the use of injective molding as a manufacturing process. Those occur depending on the efficiency of the various operations involved in the production stages. Some of the primary defects include blistering, gas burns and flashes that may appear due to the presence of contaminants. Due to the risk of their presence or occurrence, it becomes necessary to find a way to measure and detect their presence in a product, and thus minimize the compromise in quality. The problem statement and goals were given as below;

Problem statement; Excessive flash is sometimes crested on the surface of a bulldog during the injection molding process

Objective; To minimize the rate of occurrence of flash defects on bulldogs during the manufacturing process.

The process of detecting and eliminating defects in a product follows principles of the Six Sigma, which is a data-driven and disciplined approach to quality control. The DMAIC tool was used in the case study. This model comprised of the five steps of define, measure, analyze, improve and Control with the objective in mind being to determine the negative factors and decide on the most appropriate course of action. To improve the efficiency, however, different tools were employed for each phase. Those processes are discussed below.

Defining phase;

The defining stage is the most basic in any experiment as it sets the foundation on how the whole process should proceed and what to expect from the entire exercise. It is here where the group identified the specific goals of the study and defined the defects to be looked for. In this case, it was decided that looking for flashes was the most appropriate choice. The extent and natures of the defects to be identified were also defined at this stage. Furthermore, the criteria to be used in conducting the entire exercise were decided in this phase, as well as the responsibilities of each of the involved parties. The scope of the project too was determined in this phase, as well as the design of experiment(DOE) given below.

Measurement phase;

After the definition stage, a factorial design was applied in the measurement phase. This process included first the identification of levels for use in comparison to determining the source of the problem. As such, the perimeters of the experiment was thus designed to address the identified issue. The number of trials to be undertaken to establish a sample was decided here. Following this, the operation was set in motion, first with the establishment of a control sample. Four Bulldogs were produced after taking ten prior runs made to stabilize the machine. Flashes were then measured in each of them and the results then recorded in millimeters. Averages were then taken to provide data for analysis.


In the next step, the design of experiment(DOE) method for analysis. The value analysis was done from the data recorded in the measurement phase. Here the use of R&R gage tool was decided upon to determine the consistency of measurements taken and gage the sensitivity of the adopted system. In its application, three appraisals were done for ten bulldog samples and the Process Cycle Efficiency calculated, and it was determined to amount to a value of 90. Theories were after that developed in an attempt to address the root of the problem. The results obtained from this process informing of the probable cause of the problem was henceforth presented in graphs and charts for easy understanding.


ANOVA tools were employed for the improvement phase of the project, having analyzed the probable factors and the ground set for a pilot project as pertaining the goals that were formulated earlier. This was used in an attempt to develop an implementation plan for our project.


Finally, factorial design and the residual plot factors were applied to determine the most appropriate control measures. Those would then be presented to the company, and a feedback system developed to monitor the results thereafter.


Gage R&R Excel Template and Explanation - DMAIC Tools. (2018). Retrieved 24 April 2018, from

Malloy, R. A. (1994). Plastic part design for injection molding(pp. 47-85). New York: Hanser Publishers.

PMPA - Lean Six Sigma Tools and Methods. (2018). Retrieved 24 April 2018, from's-quality---lean.pdf?sfvrsn=0

Raisinghani, M. S., Ette, H., Pierce, R., Cannon, G., & Daripaly, P. (2005). Six Sigma: concepts, tools, and applications. Industrial management & Data systems, 105(4), 491-505.

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